A senior female Pakistani politician has been shot dead outside her home in the southern city of Karachi.

Zahra Shahid Hussain, 59, was the senior vice-president of Pakistan's Movement for Justice (PTI) party, led by former international cricketer Imran Khan.

She "was leaving her home for some work when three gunmen attacked her. She thought they wanted to snatch her purse and handed it over to them but they killed her", Firdous Shamim, a local PTI leader, told AFP.

Police said all three gunmen escaped after the attack.

"They shot her with one bullet near her chin and she could not survive," senior police official Nasir Aftab told AFP.

There was no immediate claim of responsibility for the attack.

Former MP and party official Arif Alvi says Hussain was an asset to the party.

"I believe the Government should investigate this murder, look for the killers, and get them sentenced," he said.

"But unfortunately over the last five years nobody has ever been arrested for the killings or tried in a court of law."

Correspondents say reports of Hussain being shot twice in the head raise suspicions that it was a targeted killing made to look like a robbery.

Mr Khan has blamed the city's dominant Muttahida Qaumi Movement (MQM) party for the murder, a claim the party has denied.

Tensions have been running high between PTI and MQM after Mr Khan's party accused the MQM of widespread vote-rigging.

Hussain's murder came on the eve of a highly-contested partial election re-run in the area after last week's general election.

MQM denies vote-rigging and has announced a boycott of the re-election.

Last weekend's election saw about 50 million Pakistanis vote, with centre-right former prime minister Nawaz Sharif emerging the winner nearly 14 years after he was deposed in a coup.

The Taliban, which denounces democracy as un-Islamic, killed more than 150 people during the election campaign, including 24 on polling day.